A hot air balloon with a volume of 12.0 m3 is initially filled with air at a

Question:

A hot air balloon with a volume of 12.0 m3 is initially filled with air at a pressure of 1.00 atm and a temperature of 19.0°C. When the balloon air is heated, the volume and the pressure of the balloon remain constant because the balloon is open to the atmosphere at the bottom. How many moles are in the balloon when the air is heated to 40.0°C?